1. Field of the Invention
The present invention relates to a radio frequency unit suitable to be applied to an RF switch, etc. that is used for a television receiver.
2. Description of the Related Art
FIG. 8 is a perspective view of a conventional radio frequency unit, and FIG. 9 is a sectional view taken along C-C of the invention. Next, the configuration of the conventional radio frequency unit will now be described with reference to FIGS. 8 and 9. A box-shaped chassis 51 made of a metal plate includes a front plate 51a, top and bottom plates 51b and 51c bent rearward from the top and bottom positions of the front plate 51a, a rear plate 51d provided between the top and bottom plates 51b and 51c, a side plate 51e that blocks up one side face of the chassis 51, an open portion 51f provided at the other side face of the chassis 51, a plurality of downwardly extending attachment legs 51g, and an attachment portion 51j provided at the front plate 51a and having a hole 51h. 
Each of first, second, and third coaxial connectors 53, 53, and 54 has an external conductor 55, and a central conductor 57 attached to the inside of the external conductor 55 via an insulator 56. Among them, the first and second connectors 52 and 53 are attached to the front plate 51a with an attachment portion 51j therebetween, and the third connector 54 is attached to the side plate 51e. 
Although not shown, an insulating board 58 is provided with a wiring pattern, and electronic components loaded on the insulating board 58. As shown in FIG. 9, the insulating board 58 is housed into the chassis 51 through the open portion 51f with a clearance K between itself and the chassis 51.
The insulating board 58 is attached between the front plate 51a or rear plate 51d of the chassis 51 and grounding wiring pattern with solder 59, and the central conductor 57 is connected to a wiring pattern for signals with solder.
Further, when a cover 60 is attached to the chassis 51 so as to cover the open portion 51f, and the chassis 51 is shielded, a conventional radio frequency unit is formed.
In the conventional radio frequency unit having such a configuration, as shown in FIG. 8, the first and second connectors 52 and 53 are respectively inserted through two insertion holes 61a provided in a chassis 61 of an electric appliance, a screw 62 is screwed into a hole 51h through a hole 61b of the chassis 61 in a state the attachment portion 51j is matched with the rear face of the chassis 61, and the attachment legs 51g are attached to a sub-board of an electrical appliance (not shown). Further, the third connector is connected to a fourth coaxial connector 64 attached to the chassis 61 via a coaxial cable 64 and a fifth connector 65. (For example, refer to JP-A-2003-123913).
However, in the conventional radio frequency unit, the insulating board 58 is attached between the front plate 51a or rear plate 51d of the chassis 51 and the grounding wiring pattern with the solder 59. Therefore, if a temperature change occurs under a use environment, the chassis 51 made of a metallic material and the insulating board 58 made of an insulating material have different coefficient of thermal expansion. Therefore, due to a difference in expansion or contraction between the chassis 51 and the insulating board 58, there is a problem in that the solder 69 between the chassis 51 and the wiring pattern is peeled off, and grounding of the wiring pattern becomes insufficient.